A wind power generation system generally includes a wind plant having a plurality of wind turbine generators supplying power to an electrical grid. Collective power output of the wind plant is greatly influenced by wind conditions on individual wind turbine generators. Grid operators often have other power resources, such as thermal power plants to balance power generation and consumption, thus accommodating variability in wind conditions during intermittent wind conditions. Thermal power plants may include, for example, coal and gas fired stations. Power fluctuation of wind farms due to gusty or low wind conditions is usually dealt with by grid operators by adjusting power output of these thermal power plants to provide sufficient power to match demands.
Electrical grids transmit and distribute energy from power plants to industrial, commercial, residential and other end-users. Grids must be operated to maintain the power balance and frequency of the grid within set range limits. Operating within the predetermined range assures that power is available to end users within the grid, as well as possibly allowing for power exchange with another grid.
In order to operate the grid within an established range, the operator of the grid must be aware of the amount of power consumed by end-users, and that generated by power plants and exchanged with neighboring systems. The operator modifies total power generation to match the changing levels of power consumption and exchange. The operator accomplishes this by instructing power plants to increase or decrease their power output.
The grid operator provides a centralized control known as automatic generation control (AGC), which instructs a participating subset of individual power generators to adjust their output to maintain a predetermined frequency and power exchange, even as power consumption varies. Grid operators must continuously fine-tune the match between power generation, grid import and grid export and power consumption. This grid regulation requires power plants that can ramp power up or down under real time control of the grid operator. Regulation is used to assure that the grid operation in the grid-operator's control area complies with a performance standard required by a power grid oversight agency. The measure of quality of grid operation in a control area is called area control error (ACE).
ACE is a combination of the control area's deviation from scheduled net import or export of power and the control area's contribution to power variation needed to maintain the grid frequency at its target level of 60 Hz in the US. Other grid frequencies are maintained in different parts of the world. The magnitude of ACE and the power needed to keep ACE within prescribed limits is small relative to the total power consumed in the control area. For example, in California, it is typically about 0.5%.
As a guide to performance, the North American Reliability Council (NERC) has defined minimum Control Performance standards (CPS1, CPS2) that quantify performance as a relationship between ACE and interconnection frequency. Rapid and widely varying loads can adversely affect a control area's control performance by NERC's control performance standards, CPS1 and CPS2. For operational reliability of the interconnection, certain penalties can be imposed on a control area when it fails to comply with NERC's standards.
When wind power is added to a system control area, the system must respond to fluctuations of both system load and wind power. Fluctuations from wind power may occur rapidly. However, it is often difficult to change power output of thermal power plants as rapidly to compensate for the contribution from wind energy. The speed at which thermal power generators can increase or decrease their power output is limited by the physical capability of various plant components. The limit on increasing power output may be different from the limit on decreasing power output. The nature of wind generation is such that a wind plant can be ordered to decrease power output, but not increase power output, since the wind is uncontrollable. Therefore, the ability to decrease wind generation may be of use when thermal power plants are decreasing at their fastest rate, and that rate is not sufficient to meet the grid operator's needs.
Grid operators must continuously vary power production from power plant generators in order to maintain a balance between load and generation, and thereby hold constant system frequency and power exchange with neighboring grids, also referred to as power ties. Relatively fast, centralized control by the AGC instructs participating individual generators to adjust their output. Wind generation has not typically participated in AGC. In power system grids for which a significant fraction of the total generation is wind, grid control objectives for maintaining frequency may be violated due to an inability of the individual generators participating in AGC to respond adequately.
Additionally, it is important to operate the wind plant at peak energy production to reduce cost to the wind plant operator. If wind plant power generation must be curtailed so as not to exceed or violate energy contribution limits to the grid, the grid operator would like to be provided with as much information as possible so as to minimize lost energy production while still operating the grid within system frequency and power exchange limits.
It is therefore, desirable to provide a system and method for sharing limited control and/or information of wind plant active power functions with the utility grid AGC to both improve the control the grid operator has over maintaining grid operations within set guidelines and to reduce wind energy production loss at the wind plant.